Telephone system



Nov. 21,1939. -o. A. PEARCE- 2.1803453" TELEPHONE SXSTEI I Filed Ilay 20, 1937 o f shame /NVENTOR v Owe/v Aws PEARCE I Patented Nov. 21, 1939 2,180,963 TELEPHONE SYSTEM Owen Avis Pearce, Barnston, England, assignor to Associated Telephone & Telegraph Company, Chicago, lilL, a corporation ofi Delaware Application May 20, 193'}, Serial No. 143,653

In Great Britain. June 15, 1936 v 20 Claims (01179- 26) The present invention relates to telephone systems. and is more particularly concerned with systems in which a group of subscribers are served for both incoming and outgoing calls by a single two-conductor line extending to the exchange. The chief object of the invention is to provide what may be termed a lockout party line system capable of serving up to 10 subscribers in one group and suitable for either manual or automatic working and which, in addition to providing complete secrecy of communication, quality of transmissionequal to that of ordinary individual line subscribers. and individual metering of outgoing calls, gives facilities for local intercommunication between the various subscribers and the possibility of group calling and also displays a visual busy indication when the line is engaged.

According to one feature of the invention in a telephone system having a plurality of stations connected to a common line extending to an exchange from which the setting up of all connections is efiected, at each station an electromagnetic step-by-step switch is connected between one conductor of the line and earth in series with a neon tube and the magnets of all the switches are operated in synchronism by high voltage impulses transmitted from the exchange overthat line conductor. 7

According to another feature of the invention in a telephone system having a plurality of parties associated with a common line extending to an exchange from which the setting up of all connections is efiected, the equipment for each station includes two step-by-step rotary switches adapted to be operated by impulses from the exchange to complete incoming and outgoing calls respectively.

-A further feature of the invention is that ina telephone system having a plurality of stations associated with a common line extending to; an exchange from which the setting up of all connections is effected, indicator devices providedat each station for indicating when the line is in use are arranged to be directly operated by impulses transmitted from theexchange for operating step-by-step switches by means of which the appropriate station is associated with the line.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawing, which shows a circuit dia gram of the equipment required at the station of each subscriber in the group.

One two-conductor line extending from the exchangeis provided per group of subscribers, the

apparatusfor each subscriber in the group being connected across the, line. In addition to the ordinary telephone each subscriber is provided with. an electromagnetic indicator, for. instance of the eye-ball type, which may. be accommodated in any suitable position where it will be easiy seen i by the subscriber. The individual switching equipment required also: includes a gas discharge device such as a neontube and two step-by-step impulse responding devices.

At the main exchange a switching unit isintroduced between the line and the usual line and cutroff relay assembly, and this unit also includes a stepping switch which serves to count or control the impulses received or transmitted .on calls between. the mainexchange and the group of subscrlbers. British Patent No. 452,038 which relates to a somewhat'similar system discloses a type of unit which could. be simply modified to operate with the apparatus required in the system about to be described.

Referring now to the drawing it willbe understood that each subscriber is provided with two step-by-step electromagnetically-operated switches F and C, each having 12 positionsassuming the line serves 10 subscribers. The first position is the home position, the second is reserved fora purpose to be described later and of the other ten positions, a different position is allocated to each subscriber. Two cams are mounted on the driving shaft, one ofwhich serves to operate the oiT-normal springs whenthe switch steps from the. home position while the other cam is arranged to operate: other springs in the particular position of the switch for the subscriber concerned; Thus the switches associated with 'No. l subscriber will operate these springs in position 3 only, while the switches associated with No. 2 subscriber will operate these springs in position t only and so on up above-mentioned British patent it will sufiice' for the purpose of the description to say that an earthed relay shunted by a rectifier is connected to the A leg by wayoi a changeover contact while.- another relay connected to batteryis extended on to the B leg by way of a changeover contact not shownbut in View of the disclosure of the I attempt to originate a call.

On the completion of the loop, the relay connected to battery-operates and locks in a local circuit while the earthed relay does not operate in this condition since it is shunted by the rectifier in a conductive direction. The changeover contacts on the B leg at the exchange are now operated and high potential pulses of the order of volts positive to earth are thereupon connected to the B wire and extended to all the party line subscribers equipments in parallel. In response to each pulse the neon tube NT associated with each station in the group is caused to strike and allows current to flow thereby causingthe switch F of each subscriber to respond since the rectifier MBA in series therewith is in a conductive direction whilst the rectifier MRC in parallel is in a non conductive direction. Rectifier MRB however is in a non-conductive direction so that the C switches will not respond to the pulses.

When the first pulse is received, each F switch magnet is energized in series with the indicator MPI thereby stepping the switch from the home position I toposition 2 while each indicator which is preferably of the magnetically-polarised eye-ball type is operated to give a visual indication of the engaged condition of the'line. The off-normal springs F(N) of each F switch are now operated and at contacts F(N)! short-circuit the indicator lvlPI and remove rectifier MRC from across the F magnet while contacts F(N) 2 disconnect the calling loop from across the line and at the same time contacts F(N)2 of other subscribers prevent them looping the line if they Conveniently it is arranged that the indicator is quicker to operate than the switch magnet F and that after operation the indicator cannot be reset until a potential negative to earth is applied. All indicators will therefore remain operated throughout the call to give a busy indication.

On the reception of the second pulse, the F switches are stepped to position 3 whereupon the contacts Fl and F2 on the switch associated with subscriber No. 1 are operated. Assuming that this subscriber has not originated the call, no loop by way of his instrument is connected across the line since his switch-hook contacts are not operated and therefore the transmissionof setting pulses from the exchange will not be stopped. If however, No. 4 subscriber has initiated the call, when all F switches are subsequently stepped to position 6 on receipt of the fifth pulse from the main exchange, a loop will be connected across the line by way of contacts F2 of the switch associated with subscriber No. 4, dial impulse contacts -IMP, the telephone instrument, contacts Fl and the switch-hook contacts SHl. The fifth positive pulse applied to the B line therefore extends via this loop on to the A line and thus-operates the earthed relay connected thereto in the main exchange since the rectifier bridged across this relay is now non-conductive. In response to the operation of this relay the transmission of pulses from the exchange is stopped. Although all F switches are set into position 6 only the F switch associated with No.

4 subscriber is arranged to operate its contacts Fl and F2 in this position and thus one telephone instrument only will be bridged across the line. Meanwhile in the main exchange it will be understood that another step-by-step switch of ordinary type has been rotated in synchronism and this will also be set in position 6 assuming that its home position is designated I. This switch serves to effect individual metering of outgoing calls on an automatic main exchange and in the case of a manual exchange it serves to indicate to the operator which subscriber in the group has originated the call.

On energisation of the earthed relay at the main exchange the A and B leads are connected through to an ordinary line'relay equipment to give a signal to the operator or to prepare the automatic equipment for receiving dialled digits. The subscriber now repeats the number to the operator or dials the digits required and the connection is extended through. The visual engaged indication will be maintained throughout the call and it is impossible for any other subscriber in the group to listen in to the conversation.

At the end of conversation, when the calling subscriber hangs up, the switching unit at the main exchange is caused to apply a plurality of high potential positive pulses to the B line whereupon all F switches will be stepped in synchronism until they again reach the home position I when the contacts F(N) l and F(N) 2 will be restored to normal. Rectifier MRC will now be bridged across the winding of each F switch magnet and serves as a short-circuit during the break period between pulses thereby holding the magnets operated to prevent the switches from being stepped past this position. The number of pulses transmitted is aranged to be at least equal to the maximum number required to home the F switches from any position and when the sending out of these homing pulses is completed the F switch magnets will restore. A plurality of pulses at a potential of the order of 100 volts negative to earth is now transmitted over the B line thus causing each neon tube NT to flash again on the extension of each pulse while each rectifier MRB will now be in a conductive direction and each rectifier MBA in a nonconductive direction. The C switches associated with each subscriber now respond and on the receipt of the first negative pulse the busy indicators MPI are caused to reset and remain in this condition until a positive pulse is again applied on initiation or reception of a further call. The C switches are now stepped completely round to the home position where the magnets lock in the manner described until the train of negative pulses is completed. All the subscribers and main exchange equipment is now normal in readiness for further calls. 1

Considering now an incoming call to one of the group subscribers, when the final selector or operator selects the desired party, a single high potential positive impulse is delivered initially to the B line to cause the indicators MP1 to give a visual engaged signal to each subscriber and at the same time to step the F switches to position 2, in which no contacts apart from the 011- normal contacts are operated on any of the F switches. A number of selecting pulses of high negative potential are now applied to the B line, the number being in accordance with the particular subscriber required. The C switches now respond due to the polarity of the potential applied while the indicators cannot be reset since they are short-circuited by contacts F(N) l. On the completion of the train of pulses, contacts Cl and 02 on the switch associated with the wanted subscriber are arranged to operate whereupon the earthed bell of this subscriber is con-' main exchange and the bell of the wanted sub-' scriber only will ring. -When he removes his receiver, contactsSHI and SH2 operate to disconnect the bell and connect a loop across the line thereby tripping the ringing. Conversation now proceeds. -At the conclusion of conversation a plurality of positive pulses is first extended over the B line to home the F switches as before and subsequently a plurality of negative pulses is extended to restore the indicators and to home the C switches the indicators in this case being restored by the next negative pulse after theC switches reach normal position.

Should a party line subscriber desire tocall another subscriber on the sameli-ne, he first calls the exchange in the usual-manner whereupon all F switches are set to a position in accordance with the number of the particular subscriber calling and the indicators are set to give a busy indication. In the case of a manual exchange the required number is then given to the operator while in the case of an automatic exchange the dialling of the number of another subscriber on the same line causes the call to be extended to a revertive calling switch which is suitably set by further dialling. The calling subscriber now hangs up and the exchange equipment transmits the required number of negative pulses over the B line to step all C switches to the position corresponding to the wanted party; The indicators however are unaffected since they are shortcircuited by the off-normal contacts 'F(N) l l. of each switchF. At the end of the negative pulse train the C switch associated with the wanted subscriber closes its contacts Cl and C2 and thereby extends his earthed hell on to the A line. It will be remembered that the F switch associated with the calling subscriber will also have operated contacts Fl and F2 and since his receiver is already restored his bell also will be connected to the A line. On application of ringing current, the bells of both the calling and called subscribers will thus be rung in parallel and when they reply their telephones will be connected in parallel to the main exchange and conversation may proceed. On the completion of conversation the usual series of positive and negative pulses are extended to home theF and C switches and to reset the indicators.

It will be noted that the earthed switching equipment associated with each subscriber is connected to the B line by way of a neon tube NT which in its non-conductive state during speaking conditions serves to isolate this equipment from the line thereby preventing the standard of speech transmission from being lowered.

In case the line limits obtainable with directly impulsed stepping switches should prove to be insufiicient, use might be made of spring-driven escapement-type switches, which would be wound up after each call. Two magnets F and C would be provided for each subscriber as before and each in responding would allow a spring driven escapement wheel to rotate a cam shaft step-by-step to bring about the closure of particular contacts as described hereinbefore. At the end of the call all F and C magnets would receive, in the normal manner, a plurality of homing pulses and on reaching the home position arrangements would be made, by virtue of the fact that the driving springs would be unwound, to bring about the closure of a pair of contacts in order to connect up a so-called winding. magnet to the A leg. On completion of the transmission of the homing pulses a suitable negative potential would then be applied for a predetermined period at the exchange switching unit to this leg and would cause 'the winding magnet to operate in a self-interrupted circuit and rotate a ratchet wheel in order to wind up the driving springs through suit- I able gearing, the winding-up time involved and the power available being dependent on the gear ratio andthe potential applied. On the completion of thewvindingmp operation the contacts mentioned above would be again opened, thereby disconnecting the winding magnet energising circuit. All apparatus would'then be ready for further use.

It will be appreciated that with the above described arrangement'the line limits. obtainable would be greatly increased'due to the escapement action of the F and C magnet armature.

I claim: 7 I

1. In -a telephone systemya" plurality of stations, a line common to said stations, an exchange at the termination of said line for setting up all connections, each's'tation having an electro-magneti'c' step-by-stepswitch and a gas discharge device arranged in a series circuit between one line conductor and earth for completing a connectionirom the station to theline, the switches of all said stations responsive to high-potential impulses transmitted over' said conductor from, said exchange' 2. In a telephone system, a plurality of 'sta tions, 21. line common to said station's, an exchange at theterminationof said line for setting up all connections, each station having an electro-magnetic step-b-y-step switch and speaking equipment, said speaking equipment normally completely disconnected from the line and adapted to be connected to the line throughcontacts of the associated stepeby step switch in accordance with a particular position of said switch,

nections, a plurality of step-by-step rotary switches'comprising two groups of switches each of which include a switch for each station, incoming or outgoing calls connected by one or the other of said switch groups, respectively, in accordance with a characteristic current transmitted from the exchange.

4. In a telephone system, a plurality of stations, a line common to said stations, an exchange at the termination of said line for setting up all connections, equipment at each of said stations including two step-by-step rotary switches operated by impulses from the exchange to connect said stations to said line for incoming and outgoing calls, respectively.

5. In a telephone system, a plurality of stations,

which each station has another step-by-step switch arranged in a series circuit with said gas g discharge device between one line conductor and earth for completing a connection from the line to the station.

'7. A telephone system as claimed inclaim 2,

inwhich each station is equipped with separate step-by-step switches for completing incoming and outgoing calls.

8. A telephone system as claimed in claim 4, in which both of said step-by-step rotary switches at each station are operated on every call.

9. A telephone system as claimed in claim 4, in which the impulses operating said switches are of opposite polarity in accordance with the switches to be operated.

10. A telephone system as claimed in claim 5, in which the first impulse from the exchange effects operation of all busy indicators.

11. A telephone system as claimed in claim 5, in which the busy indicator is operated by an impulse of either polarity and returned to normal by an impulse of opposite polarity.

12. A telephone system as claimed in claim 5, in which operation of any of said switches prevents further operation of busy indicators.

13. A telephone system as claimed in claim 3, in which a preliminary pulse is always transmitted from the exchange to the group of switches associated with outgoing calls.

14. A telephone system as claimed in claim 4, in which said switches are stepped to normal position in turn in response to impulses transmitted from the exchange on termination of a connection.

15. A telephone system as claimed in claim 4, in which other impulses from the exchange step said switches to normal position in turn on termination of a connection, the operating magnets of said switches are shunted in normalposition to maintain said magnets steadily energized until said other impulses cease.

16. A telephone system as claimed in claim 2, in which said contacts of said step-by-step switch are operated by a cam of the switch in only one of its off-normal positions which position is different in the switches associated with each of said stations.

17. In a telephone system, a plurality of stations, a line common thereto, an exchange at the termination of said line for setting up all connections, each station having a transmission circuit normally completely disconnected from the line and a selecting circuit controlled from the exchange for establishing a connection between said transmissioncircuit and the line.

18. A telephone system as claimed in claim 17, in which the selecting circuit of each station comprises a gas discharge device associated with a parallel arrangement of two electro-magnetic rotary switch-es respectively responsive to pulses of opposite potential.

19. A telephone system as claimed in claim 17, in which said selecting circuit including a gas discharge device is responsive to high potential impulses transmitted from the exchange.

20. In a telephone system, a remote station, a line extending thereto, said station having a telephone set disconnected from the line, a blocking device having a resistance characteristic such that when said device is subjected to an increasing potential its resistance decreases sharply after a predetermined potential has been reached, and a selecting device connected to the line through said blocking device and controlled over the line only by current producing at said blocking device a potential higher than said certain potential, said blocking device preventing said selecting device from being afiected by transmission of speech currents over said line.

OWEN AVIS PEARCE. 

